Heretofore, a semiconductor device which includes a CMOS circuit having a PMOS transistor and an NMOS transistor has been known.
In recent years, in order to improve the carrier mobility of a PMOS transistor, a technique has been proposed in which a compressive stress film is formed to cover the PMOS transistor so as to apply a compressive stress to the channel region thereof.
In addition, in order to improve the carrier mobility of an NMOS transistor, a technique has also been proposed in which a tensile stress film is formed to cover the NMOS transistor so as to apply a tensile stress to the channel region thereof.
However, when a compressive stress film and/or a tensile stress film is simply formed, there has been a problem in that electrical properties of the transistor are not always sufficiently improved.